<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .box1{
            width: 200px;
            height: 200px;
            background-color: #bbffaa;
        }
        /*.box1::before{*/
        /*    content: '';*/
        /*    display: table;*/
        /*}*/
        .box2{
            width: 100px;
            height: 100px;
            background-color: orange;
            margin-top: 100px;

        }
        /*clearfix 这个样式可以同时解决高度塌陷和外边距重叠的问题
            如果在遇到这些问题时,直接使用clearfix这个类即可
         */
        .clearfix::before,.clearfix::after{
            content: '';
            display: table;
            clear: both;
        }
    </style>
</head>
<body>
<div class="box1 clearfix">
    <div class="box2"></div>
</div>
</body>
</html>